The present invention relates generally to hot-gas cleanup systems and more particularly to filter holder and gasket assemblies that provide particulate barrier seals between the body of a candle filter element and the filter holder when coupled to a hot gas cleanup system support plate.
Modern industrial methods have resulted in a need for an apparatus that is capable of efficiently filtering high temperature combustion gases containing particulate material. In combustion turbine applications, for example, a combustion turbine uses energy generated from hot pressurized combustion gases produced by burning natural or propane gas, petroleum distillates or low ash fuel oil. When coal and other solid fuels are burned, particulates carried over from the combustion of such solid fuels can cause turbine blade erosion and fouling. An efficient system for filtering of such hot combustion gases would permit the use of such solid fuels. Examples of such filtering apparatus and systems can be found in U.S. Pat. Nos. 5,433,771 and 5,876,471, both of which are incorporated in their entirety herein by reference.
It is therefore desirable to provide a filtering apparatus that can filter high temperature, high pressure, aggressive gases, such as oxidizing gases, and/or reducing gases. It is also desirable to provide an improved filter holder and gasket assembly that can be employed with a conventional candle filter that can be more securely and more conveniently mounted within a pressure vessel as compared to previous filter holder and gasket assemblies.
Referring to Prior Art FIG. 1, conventional fixturing of hot gas particle filters using ceramic candle filter elements typically involves the use of two gaskets. One gasket 14 is commonly made donut-shaped with a ceramic cloth outer wrap and filled with a ceramic fiber mat. This gasket 14 is positioned directly above the top flange of the ceramic filter 11 and directly below the spacer ring 10 of a fail-safe regenerator device 8. The fail-safe regenerator device 8 functions to filter particulates from the combustion or gasification system during a filter failure event. It also functions as a heat exchanger during back pulsing to warm back pulse gas en route to the filter, thereby reducing thermal shock. A second gasket 16 is commonly made ring-shaped out of ceramic blanket material. This second gasket 16 is positioned directly below a counter-bored land inside of the filter element holder 1 and directly above the flange of the spacer ring 10. Both of these gaskets 14,16 must resist leakage. If gasket 14 leaks, particulates can bypass the filter element 11 to the clean side of the filter, thereby causing clogging of the fail-safe regenerator device 8 and loss of filter element effectiveness. Also, to the extent that the fail-safe is not an effective barrier to particulates, leakage can cause undesired particulate loading to the downstream gas turbine and undesired stack emissions. If gasket 16 leaks, particulates can bypass both the filter element 11 and the fail-safe regenerator device 8. The sock 12 and the lower donut 15 do not act as gaskets or seals but provide a cushion between metal and ceramic materials.
In addition, current fixturing of fail-safe regenerators involves wrapping a ceramic cloth material (wrap) around the body of the fail-safe regenerator and securing it in position with tape so that the fail-safe regenerator can be inserted by a friction fit into the bore of the filter holder. The wrap provides sufficient friction against the bore of the filter holder to overcome the weight of the fail-safe regenerator and to hold the component in place while the installer then inserts the candle filter, associated gasketing and other filter components. The fail-safe regenerator is held in place during operation only by the modest frictional forces described above coupled with the mechanical compression of the gaskets positioned above and below the top flange of the candle filter.
To the extent that gaskets in the filter assembly lose resilience during high temperature exposure in a filtering operation, the effectiveness of the friction fit can be reduced. Also, during reverse flow back pulse cleaning, a downward force is exerted on the candle filter and the lower gasket which can permit undesirable downward motion of the fail-safe regenerator. During pulsing, compression is also momentarily reduced in the top gasket that is located between the counter-bore of the filter holder and the bottom flange of the fail-safe regenerator. Frequent disintegration of this gasket (and of the wrap around the fail-safe regenerator body) is often attributed to insecure fixturing of the fail-safe regenerator and the candle filter.
What is needed therefore is an improved gasket design that provides an additional gasket to provide a more effective barrier to particulates during filtering operation. What is also needed is an improved structure for securing the fail-safe regenerator within the filter holder assembly. Rather than rely on the friction fit of the wrap and the compression of filter gaskets, the fail-safe regenerator needs to be held more securely in place.
The filter assembly of the present invention is provided for holding a candle filter element within a hot gas cleanup system pressure vessel. The assembly includes a filter holder having a peripheral sidewall that defines an interior chamber therein and an annular spacer ring positioned within the interior chamber. The filter assembly of the present invention includes at least one top donut gasket separate and apart from the filter holder. The top donut gasket is formed to be positioned on the filter flange end top surface for providing a seal between the annular spacer ring and the filter flange top surface. In addition, a metal bottom clamp is positioned around the filter body between the sleeve gasket and the filter holder. The metal bottom clamp can have an angled land surface thereon extending away from the sleeve. Also, at least one cushion separate and apart from the filter holder is positioned between the sleeve gasket and the filter holder sidewall on the land surface to provide a compliant separation between a portion of the filter body and the filter holder sidewall.
The assembly of the present invention further includes at least one bottom ring gasket positioned in an annular groove formed in a portion of the metal bottom clamp. The annular groove is located at a junction between an extended bottom portion of the filter holder and a radially extending portion of the metal bottom clamp.
In another aspect of the present invention, a locking groove is formed in an inner surface of the filter holder. The locking groove can have at least two portions formed in communication with the interior chamber. The locking groove can include a first axial groove portion and a second circumferential groove portion in communication with the first axial groove portion. The locking groove portions are structured to receive a tooth or teeth, such as a tooth or teeth formed integrally with an outer surface of a fail-safe regenerator device.